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1.  Phenols in Leaves and Bark of Fagus sylvatica as Determinants of Insect Occurrences 
Beech forests play an important role in temperate and north Mediterranean ecosystems in Greece since they occupy infertile montane soils. In the last glacial maximum, Fagus sylvatica (beech) was confined to Southern Europe where it was dominant and in the last thousand years has expanded its range to dominate central Europe. We sampled four different beech forest types. We found 298 insect species associated with beech trees and dead beech wood. While F. sylvatica and Quercus (oak) are confamilial, there are great differences in richness of the associated entomofauna. Insect species that inhabit beech forests are less than one fifth of those species living in oak dominated forests despite the fact that beech is the most abundant central and north European tree. There is a distinct paucity of monophagous species on beech trees and most insect species are shared between co-occurring deciduous tree species and beech. This lack of species is attributed to the vegetation history and secondary plant chemistry. Bark and leaf biophenols from beech indicate that differences in plant secondary metabolites may be responsible for the differences in the richness of entomofauna in communities dominated by beech and other deciduous trees.
PMCID: PMC3116155  PMID: 21686149
Fagus sylvatica; entomofauna; phenolics; secondary plant chemistry; insect traps; clustering; discriminant analysis
2.  Greater accumulation of litter in spruce (Picea abies) compared to beech (Fagus sylvatica) stands is not a consequence of the inherent recalcitrance of needles 
Plant and Soil  2012;358(1-2):349-369.
Background and aims
Replacement of beech by spruce is associated with changes in soil acidity, soil structure and humus form, which are commonly ascribed to the recalcitrance of spruce needles. It is of practical relevance to know how much beech must be admixed to pure spruce stands in order to increase litter decomposition and associated nutrient cycling. We addressed the impact of tree species mixture within forest stands and within litter on mass loss and nutritional release from litter.
Litter decomposition was measured in three adjacent stands of pure spruce (Picea abies), mixed beech-spruce and pure beech (Fagus sylvatica) on three nutrient-rich sites and three nutrient-poor sites over a three-year period using the litterbag method (single species and mixed species bags).
Mass loss of beech litter was not higher than mass loss of spruce litter. Mass loss and nutrient release were not affected by litter mixing. Litter decay indicated non-additive patterns, since similar remaining masses under pure beech (47%) and mixed beech-spruce (48%) were significantly lower than under pure spruce stands (67%). Release of the main components of the organic substance (Corg, Ntot, P, S, lignin) and associated K were related to mass loss, while release of other nutrients was not related to mass loss.
In contradiction to the widely held assumption of slow decomposition of spruce needles, we conclude that accumulation of litter in spruce stands is not caused by recalcitrance of spruce needles to decay; rather adverse environmental conditions in spruce stands retard decomposition. Mixed beech-spruce stands appear to be as effective as pure beech stands in counteracting these adverse conditions.
PMCID: PMC4372834  PMID: 25834285
Decomposition; Fagus sylvatica; Litter quality; Litterbag; Mixing effects; Picea abies
3.  Does mixing of beech (Fagus sylvatica) and spruce (Picea abies) litter hasten decomposition? 
Plant and Soil  2013;377(1-2):217-234.
Background and aims
It is of practical relevance to know how much beech must be admixed to pure spruce stands in order to increase litter decomposition and associated nutrient cycling, since the formation of thick organic layers is commonly ascribed to the recalcitrance of spruce needles. We addressed the impact of tree species mixture within forest stands and within litter on mass loss and nutritional release from litter.
Litter decomposition was measured in three adjacent stands of pure spruce (Picea abies), mixed beech-spruce and pure beech (Fagus sylvatica) on a nutrient-rich site and a nutrient-poor site over a 2-year period using litterbags which were filled with five different mixtures of beech and spruce litter.
Mass loss of beech litter was not higher than mass loss of spruce litter. Decay was primarily affected by tree species composition of the incubation stand and was faster in (mixed) beech forests stands than in spruce forests, while the influence of litter species and their mixtures on decay rates was small. Net transfers of nutrients between the two litter species (direct effects) in the mixed bags were minimal, since initial beech and spruce litter did not have different litter quality. However, in a few cases indirect effects (e.g., changing decomposer abundance and activity) caused non-additive patterns for the totals within the mixed bags, hastening decomposition within the first year.
Greater accumulation of litter in spruce compared to beech stands is not a consequence of the inherent recalcitrance of needles. Adverse environmental conditions in spruce stands retard decomposition. Indirect effects on decomposition caused by stand mixture are not mimicked by litter mixtures within mesh bags.
PMCID: PMC3987168  PMID: 24744450
Decomposition; Fagus sylvatica; Litter quality; Litterbag; Mixing effects; Picea abies
4.  Does mixing of beech (Fagus sylvatica) and spruce (Picea abies) litter hasten decomposition? 
Plant and soil  2014;377(1-2):217-234.
Background and aims
It is of practical relevance to know how much beech must be admixed to pure spruce stands in order to increase litter decomposition and associated nutrient cycling, since the formation of thick organic layers is commonly ascribed to the recalcitrance of spruce needles. We addressed the impact of tree species mixture within forest stands and within litter on mass loss and nutritional release from litter.
Litter decomposition was measured in three adjacent stands of pure spruce (Picea abies), mixed beech-spruce and pure beech (Fagus sylvatica) on a nutrient-rich site and a nutrient-poor site over a 2-year period using litterbags which were filled with five different mixtures of beech and spruce litter.
Mass loss of beech litter was not higher than mass loss of spruce litter. Decay was primarily affected by tree species composition of the incubation stand and was faster in (mixed) beech forests stands than in spruce forests, while the influence of litter species and their mixtures on decay rates was small. Net transfers of nutrients between the two litter species (direct effects) in the mixed bags were minimal, since initial beech and spruce litter did not have different litter quality. However, in a few cases indirect effects (e.g., changing decomposer abundance and activity) caused non-additive patterns for the totals within the mixed bags, hastening decomposition within the first year.
Greater accumulation of litter in spruce compared to beech stands is not a consequence of the inherent recalcitrance of needles. Adverse environmental conditions in spruce stands retard decomposition. Indirect effects on decomposition caused by stand mixture are not mimicked by litter mixtures within mesh bags.
PMCID: PMC3987168  PMID: 24744450
Decomposition; Fagus sylvatica; Litter quality; Litterbag; Mixing effects; Picea abies
5.  Nitrogen Addition Enhances Drought Sensitivity of Young Deciduous Tree Species 
Understanding how trees respond to global change drivers is central to predict changes in forest structure and functions. Although there is evidence on the mode of nitrogen (N) and drought (D) effects on tree growth, our understanding of the interplay of these factors is still limited. Simultaneously, as mixtures are expected to be less sensitive to global change as compared to monocultures, we aimed to investigate the combined effects of N addition and D on the productivity of three tree species (Fagus sylvatica, Quercus petraea, Pseudotsuga menziesii) in relation to functional diverse species mixtures using data from a 4-year field experiment in Northwest Germany. Here we show that species mixing can mitigate the negative effects of combined N fertilization and D events, but the community response is mainly driven by the combination of certain traits rather than the tree species richness of a community. For beech, we found that negative effects of D on growth rates were amplified by N fertilization (i.e., combined treatment effects were non-additive), while for oak and fir, the simultaneous effects of N and D were additive. Beech and oak were identified as most sensitive to combined N+D effects with a strong size-dependency observed for beech, suggesting that the negative impact of N+D becomes stronger with time as beech grows larger. As a consequence, the net biodiversity effect declined at the community level, which can be mainly assigned to a distinct loss of complementarity in beech-oak mixtures. This pattern, however, was not evident in the other species-mixtures, indicating that neighborhood composition (i.e., trait combination), but not tree species richness mediated the relationship between tree diversity and treatment effects on tree growth. Our findings point to the importance of the qualitative role (‘trait portfolio’) that biodiversity play in determining resistance of diverse tree communities to environmental changes. As such, they provide further understanding for adaptive management strategies in the context of global change.
PMCID: PMC4957528  PMID: 27499761
climate change; complementarity; ecosystem functioning; insurance hypothesis; nitrogen deposition; plant–climate interactions; temperate forest; tree growth
6.  Variation in Ecophysiological Traits and Drought Tolerance of Beech (Fagus sylvatica L.) Seedlings from Different Populations 
Frequency and intensity of heat waves and drought events are expected to increase in Europe due to climate change. European beech (Fagus sylvatica L.) is one of the most important native tree species in Europe. Beech populations originating throughout its native range were selected for common-garden experiments with the aim to determine whether there are functional variations in drought stress responses among different populations. One-year old seedlings from four to seven beech populations were grown and drought-treated in a greenhouse, replicating the experiment at two contrasting sites, in Italy (Mediterranean mountains) and Germany (Central Europe). Experimental findings indicated that: (1) drought (water stress) mainly affected gas exchange describing a critical threshold of drought response between 30 and 26% SWA for photosynthetic rate and Ci/Ca, respectively; (2) the Ci to Ca ratio increased substantially with severe water stress suggesting a stable instantaneous water use efficiency and an efficient regulation capacity of water balance achieved by a tight stomatal control; (3) there was a different response to water stress among the considered beech populations, differently combining traits, although there was not a well-defined variability in drought tolerance. A combined analysis of functional and structural traits for detecting stress signals in beech seedlings is suggested to assess plant performance under limiting moisture conditions and, consequently, to estimate evolutionary potential of beech under a changing environmental scenario.
PMCID: PMC4916223  PMID: 27446118
water stress; ecophysiology; gas exchange; chlorophyll a fluorescence; European beech
7.  Decomposition of beech (Fagus sylvatica) and pine (Pinus nigra) litter along an Alpine elevation gradient: Decay and nutrient release 
Geoderma  2015;251-252:92-104.
Litter decomposition is an important process for cycling of nutrients in terrestrial ecosystems. The objective of this study was to evaluate direct and indirect effects of climate on litter decomposition along an altitudinal gradient in a temperate Alpine region. Foliar litter of European beech (Fagus sylvatica) and Black pine (Pinus nigra) was incubated in litterbags during two years in the Hochschwab massif of the Northern Limestone Alps of Austria. Eight incubation sites were selected following an altitudinal/climatic transect from 1900 to 900 m asl. The average remaining mass after two years of decomposition amounted to 54% (beech) and 50% (pine). Net release of N, P, Na, Al, Fe and Mn was higher in pine than in beech litter due to high immobilization (retention) rates of beech litter. However, pine litter retained more Ca than beech litter. Altitude retarded decay (mass loss and associated C release) in beech litter during the first year only but had a longer lasting effect on decaying pine litter. Altitude comprises a suite of highly auto-correlated characteristics (climate, vegetation, litter, soil chemistry, soil microbiology, snow cover) that influence litter decomposition. Hence, decay and nutrient release of incubated litter is difficult to predict by altitude, except during the early stage of decomposition, which seemed to be controlled by climate. Reciprocal litter transplant along the elevation gradient yielded even relatively higher decay of pine litter on beech forest sites after a two-year adaptation period of the microbial community.
•Mass loss is higher for pine than for beech litter.•Altitude retards decay of litter with a longer lasting effect on pine litter.•Nutrient release is predictable by altitude during the early stage of decomposition.•Net release of N, P, Na, Al, Fe and Mn is higher in pine than in beech litter.•Reciprocal litter transplant yields higher decay of pine litter on beech forest sites.
PMCID: PMC4418737  PMID: 26240437
Climosequence; Decomposition; Elevation gradient; Fagus sylvatica; Litterbag; Pinus nigra
8.  Tree Species Composition and Harvest Intensity Affect Herbivore Density and Leaf Damage on Beech, Fagus sylvatica, in Different Landscape Contexts 
PLoS ONE  2015;10(5):e0126140.
Most forests are exposed to anthropogenic management activities that affect tree species composition and natural ecosystem processes. Changes in ecosystem processes such as herbivory depend on management intensity, and on regional environmental conditions and species pools. Whereas influences of specific forest management measures have already been addressed for different herbivore taxa on a local scale, studies considering effects of different aspects of forest management across different regions are rare. We assessed the influence of tree species composition and intensity of harvesting activities on arthropod herbivores and herbivore-related damage to beech trees, Fagus sylvatica, in 48 forest plots in three regions of Germany. We found that herbivore abundance and damage to beech trees differed between regions and that – despite the regional differences - density of tree-associated arthropod taxa and herbivore damage were consistently affected by tree species composition and harvest intensity. Specifically, overall herbivore damage to beech trees increased with increasing dominance of beech trees – suggesting the action of associational resistance processes – and decreased with harvest intensity. The density of leaf chewers and mines was positively related to leaf damage, and several arthropod groups responded to beech dominance and harvest intensity. The distribution of damage patterns was consistent with a vertical shift of herbivores to higher crown layers during the season and with higher beech dominance. By linking quantitative data on arthropod herbivore abundance and herbivory with tree species composition and harvesting activity in a wide variety of beech forests, our study helps to better understand the influence of forest management on interactions between a naturally dominant deciduous forest tree and arthropod herbivores.
PMCID: PMC4418704  PMID: 25938417
9.  Drought-Adaptation Potential in Fagus sylvatica: Linking Moisture Availability with Genetic Diversity and Dendrochronology 
PLoS ONE  2012;7(3):e33636.
Microevolution is essential for species persistence especially under anticipated climate change scenarios. Species distribution projection models suggested that the dominant tree species of lowland forests in Switzerland, European beech (Fagus sylvatica L.), might disappear from most areas due to expected longer dry periods. However, if genotypes at the moisture boundary of the species climatic envelope are adapted to lower moisture availability, they can serve as seed source for the continuation of beech forests under changing climates.
Methodology/Principal Findings
With an AFLP genome scan approach, we studied neutral and potentially adaptive genetic variation in Fagus sylvatica in three regions containing a dry and a mesic site each (nind. = 241, nmarkers = 517). We linked this dataset with dendrochronological growth measures and local moisture availabilities based on precipitation and soil characteristics. Genetic diversity decreased slightly at dry sites. Overall genetic differentiation was low (Fst = 0.028) and Bayesian cluster analysis grouped all populations together suggesting high (historical) gene flow. The Bayesian outlier analyses indicated 13 markers with three markers differing between all dry and mesic sites and the others between the contrasting sites within individual regions. A total of 41 markers, including seven outlier loci, changed their frequency with local moisture availability. Tree height and median basal growth increments were reduced at dry sites, but marker presence/absence was not related to dendrochronological characteristics.
Conclusion and Their Significance
The outlier alleles and the makers with changing frequencies in relation to moisture availability indicate microevolutionary processes occurring within short geographic distances. The general genetic similarity among sites suggests that ‘preadaptive’ genes can easily spread across the landscape. Yet, due to the long live span of trees, fostering saplings originating from dry sites and grown within mesic sites might increase resistance of beech forests during the anticipated longer dry periods.
PMCID: PMC3308988  PMID: 22448260
10.  Impact of elevated atmospheric O3 on the actinobacterial community structure and function in the rhizosphere of European beech (Fagus sylvatica L.) 
Many bacteria belonging to the phylum of Actinobacteria are known as antagonists against phytpathogenic microbes. This study aimed to analyze the effect of ozone on the actinobacterial community of the rhizosphere of four years old European beech (Fagus sylvatica L.) trees during different time points of the vegetation period. Effects of ozone on the total community structure of Actinobacteria were studied based on the analysis of 16S rRNA gene amplicons. In addition effects of the ozone treatment on the diversity of potential biocontrol active Actionobacteria being able to produce antibiotics were characterized by using the type II polyketide synthases (PKS) genes as marker. Season as well as ozone treatments had a significant effect on parts of the actinobacterial rhizosphere community of European beech. However on the basis of the performed analysis, the diversity of Actinobacteria possessing type II PKS genes is neither affected by seasonal changes nor by the ozone treatments, indicating no influence of the investigated treatments on the biocontrol active part of the actinobacterial community.
PMCID: PMC3920289  PMID: 24575080
European beech; Actinobacteria; biocontrol; polyketide synthase gene; ozone
11.  Leaf litter decomposition in temperate deciduous forest stands with a decreasing fraction of beech (Fagus sylvatica) 
Oecologia  2010;164(4):1083-1094.
We hypothesised that the decomposition rates of leaf litter will increase along a gradient of decreasing fraction of the European beech (Fagus sylvatica) and increasing tree species diversity in the generally beech-dominated Central European temperate deciduous forests due to an increase in litter quality. We studied the decomposition of leaf litter including its lignin fraction in monospecific (pure beech) stands and in stands with up to five tree genera (Acer spp., Carpinus betulus, Fagus sylvatica, Fraxinus excelsior, Tilia spp.) using a litterbag approach. Litter and lignin decomposition was more rapid in stand-representative litter from multispecific stands than in litter from pure beech stands. Except for beech litter, the decomposition rates of species-specific tree litter did not differ significantly among the stand types, but were most rapid in Fraxinus excelsior and slowest in beech in an interspecific comparison. Pairwise comparisons of the decomposition of beech litter with litter of the other tree species (except for Acerplatanoides) revealed a “home field advantage” of up to 20% (more rapid litter decomposition in stands with a high fraction of its own species than in stands with a different tree species composition). Decomposition of stand-representative litter mixtures displayed additive characteristics, not significantly more rapid than predicted by the decomposition of litter from the individual tree species. Leaf litter decomposition rates were positively correlated with the initial N and Ca concentrations of the litter, and negatively with the initial C:N, C:P and lignin:N ratios. The results support our hypothesis that the overall decomposition rates are mainly influenced by the chemical composition of the individual litter species. Thus, the fraction of individual tree species in the species composition seems to be more important for the litter decomposition rates than tree species diversity itself.
PMCID: PMC2981742  PMID: 20596729
Biodiversity; Central Europe; Element ratio; Litter degradation; Litterbag
12.  Sapling herbivory, invertebrate herbivores and predators across a natural tree diversity gradient in Germany’s largest connected deciduous forest 
Oecologia  2009;160(2):279-288.
Tree species-rich forests are hypothesised to be less susceptible to insect herbivores, but so far herbivory–diversity relationships have rarely been tested for tree saplings, and no such study has been published for deciduous forests in Central Europe. We expected that diverse tree communities reduce the probability of detection of host plants and increase abundance of predators, thereby reducing herbivory. We examined levels of herbivory suffered by beech (Fagus sylvatica L.) and maple saplings (Acer pseudoplatanus L. and Acer platanoides L.) across a tree species diversity gradient within Germany’s largest remaining deciduous forest area, and investigated whether simple beech or mixed stands were less prone to damage caused by herbivorous insects. Leaf area loss and the frequency of galls and mines were recorded for 1,040 saplings (>13,000 leaves) in June and August 2006. In addition, relative abundance of predators was assessed to test for potential top-down control. Leaf area loss was generally higher in the two species of maple compared to beech saplings, while only beech showed a decline in damage caused by leaf-chewing herbivores across the tree diversity gradient. No significant patterns were found for galls and mines. Relative abundance of predators on beech showed a seasonal response and increased on species-rich plots in June, suggesting higher biological control. We conclude that, in temperate deciduous forests, herbivory–tree diversity relationships are significant, but are tree species-dependent with bottom-up and top-down control as possible mechanisms. In contrast to maple, beech profits from growing in a neighbourhood of higher tree richness, which implies that species identity effects may be of greater importance than tree diversity effects per se. Hence, herbivory on beech appeared to be mediated bottom-up by resource concentration in the sampled forest stands, as well as regulated top-down through biocontrol by natural enemies.
Electronic supplementary material
The online version of this article (doi:10.1007/s00442-009-1304-2) contains supplementary material, which is available to authorised users.
PMCID: PMC3085765  PMID: 19238448
Diversity-functioning relationships; Leaf damage; Mines; Multitrophic interactions; Plant–animal interactions
13.  Facilitative-Competitive Interactions in an Old-Growth Forest: The Importance of Large-Diameter Trees as Benefactors and Stimulators for Forest Community Assembly 
PLoS ONE  2015;10(3):e0120335.
The role of competition in tree communities is increasingly well understood, while little is known about the patterns and mechanisms of the interplay between above- and belowground competition in tree communities. This knowledge, however, is crucial for a better understanding of community dynamics and developing adaptive near-natural management strategies. We assessed neighbourhood interactions in an unmanaged old-growth European beech (Fagus sylvatica) forest by quantifying variation in the intensity of above- (shading) and belowground competition (crowding) among dominant and co-dominant canopy beech trees during tree maturation. Shading had on average a much larger impact on radial growth than crowding and the sensitivity to changes in competitive conditions was lowest for crowding effects. We found that each mode of competition reduced the effect of the other. Increasing crowding reduced the negative effect of shading, and at high levels of shading, crowding actually had a facilitative effect and increased growth. Our study demonstrates that complementarity in above- and belowground processes enable F. sylvatica to alter resource acquisition strategies, thus optimising tree radial growth. As a result, competition seemed to become less important in stands with a high growing stock and tree communities with a long continuity of anthropogenic undisturbed population dynamics. We suggest that growth rates do not exclusively depend on the density of potential competitors at the intraspecific level, but on the conspecific aggregation of large-diameter trees and their functional role for regulating biotic filtering processes. This finding highlights the potential importance of the rarely examined relationship between the spatial aggregation pattern of large-diameter trees and the outcome of neighbourhood interactions, which may be central to community dynamics and the related forest ecosystem services.
PMCID: PMC4372556  PMID: 25803035
14.  Establishment success of sooty beech scale insects, Ultracoelostoma sp., on different host tree species in New Zealand 
The sooty beech scale insect (Ultracoelostoma sp.) (Hemiptera: Margarodidae) exhibits a highly patchy distribution at local and regional scales. A major factor driving this common distributional phenomenon in other phloem-feeding insects is aggregation and local adaptation. The aim of this study was to determine if Ultracoelostoma was locally adapted to its natal host trees, by contrasting the establishment rates of first instar “crawlers” in reciprocal transfers to natal versus novel hosts. Although there are two closely-related species of sooty beech scale insect, the morphological characters of crawlers in this study were intermediate between those of U. assimile and U. brittini. However, all of the voucher specimens examined had consistent morphology, indicating that they belong to one species which we refer to as Ultracoelostoma sp. Reciprocal transfers of crawlers were carried out between individual red beech (Nothofagus fusca), as well as between mountain beech (N. solandri) and red beech trees, to ascertain if insects had become locally adapted to their individual host tree or to host species. In total, 480 crawlers were placed in enclosures on their natal and novel host trees, of which only 32 (6.7 %) became established. No evidence for local adaptation, either to individual host trees or to host tree species, was found. There was also no difference in crawler establishment between natal and novel hosts. However, crawlers originating from mountain beech trees had significantly higher establishment rates on both natal mountain beech and novel red beech hosts, than did crawlers originating from red beech trees. The superior ability of mountain beech crawlers to become established, even on novel red beech trees, suggests that scale insects on mountain beech trees have higher individual fitness (possibly due to maternal effects mediated by differences in host nutritional quality, defensive compounds or growth rate). This increased fitness may result in crawlers being better provisioned to search for appropriate establishment sites. The results of this study indicate that beech scale insects perform better on mountain beech at this site, although crawlers did not preferentially establish on mountain beech.
PMCID: PMC2990322  PMID: 19537979
honeydew; host preference; local adaptation; Ultracoelostoma assimile; Ultracoelostoma brittini; Nothofagus fusca; Nothofagus solandri
15.  Model-based analysis of avoidance of ozone stress by stomatal closure in Siebold's beech (Fagus crenata) 
Annals of Botany  2013;112(6):1149-1158.
Background and Aims
Resistance of plants to ozone stress can be classified as either avoidance or tolerance. Avoidance of ozone stress may be explained by decreased stomatal conductance during ozone exposure because stomata are the principal interface for entry of ozone into plants. In this study, a coupled photosynthesis–stomatal model was modified to test whether the presence of ozone can induce avoidance of ozone stress by stomatal closure.
The response of Siebold's beech (Fagus crenata), a representative deciduous tree species, to ozone was studied in a free-air ozone exposure experiment in Japan. Photosynthesis and stomatal conductance were measured under ambient and elevated ozone. An optimization model of stomata involving water, CO2 and ozone flux was tested using the leaf gas exchange data.
Key Results
The data suggest that there are two phases in the avoidance of ozone stress via stomatal closure for Siebold's beech: (1) in early summer ozone influx is efficiently limited by a reduction in stomatal conductance, without any clear effect on photosynthetic capacity; and (2) in late summer and autumn the efficiency of ozone stress avoidance was decreased because the decrease in stomatal conductance was small and accompanied by an ozone-induced decline of photosynthetic capacity.
Ozone-induced stomatal closure in Siebold's beech during early summer reduces ozone influx and allows the maximum photosynthetic capacity to be reached, but is not sufficient in older leaves to protect the photosynthetic system.
PMCID: PMC3783231  PMID: 23904447
Tropospheric ozone; stomatal conductance; stomatal closure; stress avoidance; photosynthesis–stomatal model; Siebold's beech; Fagus crenata
16.  Desiccation and Mortality Dynamics in Seedlings of Different European Beech (Fagus sylvatica L.) Populations under Extreme Drought Conditions 
European beech (Fagus sylvatica L., hereafter beech), one of the major native tree species in Europe, is known to be drought sensitive. Thus, the identification of critical thresholds of drought impact intensity and duration are of high interest for assessing the adaptive potential of European beech to climate change in its native range. In a common garden experiment with one-year-old seedlings originating from central and marginal origins in six European countries (Denmark, Germany, France, Romania, Bosnia-Herzegovina, and Spain), we applied extreme drought stress and observed desiccation and mortality processes among the different populations and related them to plant water status (predawn water potential, ΨPD) and soil hydraulic traits. For the lethal drought assessment, we used a critical threshold of soil water availability that is reached when 50% mortality in seedling populations occurs (LD50SWA). We found significant population differences in LD50SWA (10.5–17.8%), and mortality dynamics that suggest a genetic difference in drought resistance between populations. The LD50SWA values correlate significantly with the mean growing season precipitation at population origins, but not with the geographic margins of beech range. Thus, beech range marginality may be more due to climatic conditions than to geographic range. The outcome of this study suggests the genetic variation has a major influence on the varying adaptive potential of the investigated populations.
PMCID: PMC4906631  PMID: 27379105
Fagus sylvatica; drought; desiccation; mortality; LD50SWA; soil water availability; genetic variation; pre-dawn water potential
17.  Spatial Patterns of Ectomycorrhizal Assemblages in a Monospecific Forest in Relation to Host Tree Genotype 
Ectomycorrhizas (EcM) are important for soil exploration and thereby may shape belowground interactions of roots. We investigated the composition and spatial structures of EcM assemblages in relation to host genotype in an old-growth, monospecific beech (Fagus sylvatica) forest. We hypothesized that neighboring roots of different beech individuals are colonized by similar EcM assemblages if host genotype had no influence on the fungal colonization and that the similarity would decrease with increasing distance of the sampling points. The alternative was that the EcM species showed preferences for distinct beech genotypes resulting in intraspecific variation of EcM-host assemblages. EcM species identities, abundance and exploration type as well as the genotypes of the colonized roots were determined in each sampling unit of a 1 L soil core (r = 0.04 m, depth 0.2 m). The Morisita-Horn similarity indices (MHSI) based on EcM species abundance and multiple community comparisons were calculated. No pronounced variation of MHSI with increasing distances of the sampling points within a plot was found, but variations between plots. Very high similarities and no between plot variation were found for MHSI based on EcM exploration types suggesting homogenous soil foraging in this ecosystem. The EcM community on different root genotypes in the same soil core exhibited high similarity, whereas the EcM communities on the root of the same tree genotype in different soil cores were significantly dissimilar. This finding suggests that spatial structuring of EcM assemblages occurs within the root system of an individual. This may constitute a novel, yet unknown mechanism ensuring colonization by a diverse EcM community of the roots of a given host individual.
PMCID: PMC3633777  PMID: 23630537
belowground interactions; community ecology; ectomycorrhiza; deciduous forest; intraspecific variation; interspecific variation
18.  Girdling Affects Ectomycorrhizal Fungal (EMF) Diversity and Reveals Functional Differences in EMF Community Composition in a Beech Forest▿ † 
The relationships between plant carbon resources, soil carbon and nitrogen content, and ectomycorrhizal fungal (EMF) diversity in a monospecific, old-growth beech (Fagus sylvatica) forest were investigated by manipulating carbon flux by girdling. We hypothesized that disruption of the carbon supply would not affect diversity and EMF species numbers if EM fungi can be supplied by plant internal carbohydrate resources or would result in selective disappearance of EMF taxa because of differences in carbon demand of different fungi. Tree carbohydrate status, root demography, EMF colonization, and EMF taxon abundance were measured repeatedly during 1 year after girdling. Girdling did not affect root colonization but decreased EMF species richness of an estimated 79 to 90 taxa to about 40 taxa. Cenococcum geophilum, Lactarius blennius, and Tomentella lapida were dominant, colonizing about 70% of the root tips, and remained unaffected by girdling. Mainly cryptic EMF species disappeared. Therefore, the Shannon-Wiener index (H′) decreased but evenness was unaffected. H′ was positively correlated with glucose, fructose, and starch concentrations of fine roots and also with the ratio of dissolved organic carbon to dissolved organic nitrogen (DOC/DON), suggesting that both H′ and DOC/DON were governed by changes in belowground carbon allocation. Our results suggest that beech maintains numerous rare EMF species by recent photosynthate. These EM fungi may constitute biological insurance for adaptation to changing environmental conditions. The preservation of taxa previously not known to colonize beech may, thus, form an important reservoir for future forest development.
PMCID: PMC2837996  PMID: 20097809
19.  A Dynamical Model of Environmental Effects on Allocation to Carbon-based Secondary Compounds in Juvenile Trees 
Annals of Botany  2007;101(8):1089-1098.
Background and Aims
Patterns and variations in concentration of carbon-based secondary compounds in plant tissues have been explained by means of different complementary and, in some cases, contradictory plant defence hypotheses for more than 20 years. These hypotheses are conceptual models which consider environmental impacts on plant internal demands. In the present study, a mathematical model is presented, which converts and integrates the concepts of the ‘Growth–Differentiation Balance’ hypothesis and the ‘Protein Competition’ model into a dynamic plant growth model, that was tested with concentration data of polyphenols in leaves of juvenile apple, beech and spruce trees. The modelling approach is part of the plant growth model PLATHO that considers simultaneously different environmental impacts on the most important physiological processes of plants.
The modelling approach for plant internal resource allocation is based on a priority scheme assuming that growth processes have priority over allocation to secondary compounds and that growth-related metabolism is more strongly affected by nitrogen deficiency than defence-related secondary metabolism.
Key Results
It is shown that the model can reproduce the effect of nitrogen fertilization on allocation patterns in apple trees and the effects of elevated CO2 and competition in juvenile beech and spruce trees. The analysis of model behaviour reveals that large fluctuations in plant internal availability of carbon and nitrogen are possible within a single vegetation period. Furthermore, the model displays a non-linear allocation behaviour to carbon-based secondary compounds.
The simulation results corroborate the underlying assumptions of the presented modelling approach for resource partitioning between growth-related primary metabolism and defence-related secondary metabolism. Thus, the dynamical modelling approach, which considers variable source and sink strengths of plant internal resources within different phenological growth stages, presents a successful translation of existing concepts into a dynamic mathematical model.
PMCID: PMC2710266  PMID: 17693454
Plant growth; carbon-based secondary compounds; plant defence hypotheses; simulation model; phenolic allocation; nitrogen; carbon dioxide; Malus domestica; Fagus sylvatica; Picea abies
20.  Thirty Years of Compositional Change in an Old-Growth Temperate Forest: The Role of Topographic Gradients in Oak-Maple Dynamics 
PLoS ONE  2016;11(7):e0160238.
Ecological communities are structured in response to spatial and temporal variation of numerous factors, including edaphic conditions, biotic interactions, climatic patterns and disturbance regimes. Widespread anthropogenic factors such as timber harvesting can create long-lasting impacts, obscuring the relationship between community structure and environmental conditions. Minimally impacted systems such as old-growth forests can serve as a useful ecological baseline for predicting long-term compositional shifts. We utilized decadal tree species sampling data (1979–2010) divided into three strata (understory, midstory, overstory) to examine temporal changes in relative abundances and spatial distributions of dominant taxa, as well as overall shifts in community composition, in a relatively pristine Appalachian old-growth forest in eastern Kentucky, USA. Quercus and Carya species persisted mainly as mature canopy trees with decreasing juvenile recruitment, especially in mesic areas. In contrast, Acer, Fagus, and other mesophytic species were abundant and spatially widespread in subcanopy layers suggesting these species are more likely to recruit in gap-scale canopy openings. In the overstory, mesophytic species were spatially restricted to lower and mid-slope mesic habitats. Temporal changes in community composition were most evident in the understory and tended to be greater in mesic areas, a trend seemingly driven by recruitment failure among xerophytic species. In subcanopy vegetation we discovered a loss of distinction through time among the ecological community designations established following the 1979 survey (Chestnut oak, Mixed mesophytic, and Beech). The overstory was more stable through time, suggesting a storage effect where long-lived trees have maintained a particular community composition through time in areas where regeneration opportunities are minimal under current environmental conditions. Overall, sitewide canopy succession is occurring slowly in the absence of major disturbance, and topography-driven environmental variation appears to have an important local-scale filtering effect on communities.
PMCID: PMC4965133  PMID: 27467130
21.  Physiological Responses of Beech and Sessile Oak in a Natural Mixed Stand During a Dry Summer 
Annals of Botany  2002;89(6):723-730.
Responses of CO2 assimilation and stomatal conductance to decreasing leaf water potential, and to environmental factors, were analysed in a mixed natural stand of sessile oak (Quercus petraea ssp. medwediewii) and beech (Fagus sylvatica L.) in Greece during the exceptionally dry summer of 1998. Seasonal courses of leaf water potential were similar for both species, whereas mean net photosynthesis and stomatal conductance were always higher in sessile oak than in beech. The relationship between net photosynthesis and stomatal conductance was strong for both species. Sessile oak had high rates of photosynthesis even under very low leaf water potentials and high air temperatures, whereas the photosynthetic rate of beech decreased at low water potentials. Diurnal patterns were similar in both species but sessile oak had higher rates of CO2 assimilation than beech. Our results indicate that sessile oak is more tolerant of drought than beech, due, in part, to its maintenance of photosynthesis at low water potential.
PMCID: PMC4233840  PMID: 12102528
Sessile oak; Quercus petraea ssp.; medwediewii; beech; Fagus sylvatica L.; CO2 assimilation; stomatal conductance; leaf water potential; drought
22.  On the influence of provenance to soil quality enhanced stress reaction of young beech trees to summer drought 
Ecology and Evolution  2016;6(22):8276-8290.
Climate projections propose that drought stress will become challenging for establishing trees. The magnitude of stress is dependent on tree species, provenance, and most likely also highly influenced by soil quality. European Beech (Fagus sylvatica) is of major ecological and economical importance in Central European forests. The species has an especially wide physiological and ecological amplitude enabling growth under various soil conditions within its distribution area in Central Europe. We studied the effects of extreme drought on beech saplings (second year) of four climatically distinct provenances growing on different soils (sandy loam and loamy sand) in a full factorial pot experiment. Foliar δ13C, δ15N, C, and N as well as above‐ and belowground growth parameters served as measures for stress level and plant growth. Low‐quality soil enhanced the effect of drought compared with qualitatively better soil for the above‐ and belowground growth parameters, but foliar δ13C values revealed that plant stress was still remarkable in loamy soil. For beeches of one provenance, negative sandy soil effects were clearly smaller than for the others, whereas for another provenance drought effects in sandy soil were sometimes fatal. Foliar δ15N was correlated with plant size during the experiment. Plasticity of beech provenances in their reaction to drought versus control conditions varied clearly. Although a general trend of declining growth under control or drought conditions in sandy soil was found compared to loamy soil, the magnitude of the effect of soil quality was highly provenance specific. Provenances seemed to show adaptations not only to drought but also to soil quality. Accordingly, scientists should integrate information about climatic pre‐adaptation and soil quality within the home range of populations for species distribution modeling and foresters should evaluate soil quality and climatic parameters when choosing donor populations for reforestation projects.
PMCID: PMC5108277  PMID: 27878095
climate change; drought adaptation; Fagus sylvatica; foliar δ13C; natural stable isotope signature; plasticity
23.  Responses of beech and spruce foliage to elevated carbon dioxide, increased nitrogen deposition and soil type 
AoB Plants  2015;7:plv067.
Over four years young central European beech and spruce trees, growing on either acidic or calcareous forest soil, were exposed to elevated CO2 and nitrogen deposition as forecast for the period 2050–2100. The elevated CO2 had a positive fertilising effect on spruce foliage only, but led to an accumulation of tannins, cell wall thickening and an acceleration of cell senescence in both species. These effects were partly mediated by the soil type and nitrogen supply. Rising CO2 concentration and nitrogen deposition may have similar effects on the leaf cell physiology - mechanistically - but induce contrasting, specific growth responses.
Although enhanced carbon fixation by forest trees may contribute significantly to mitigating an increase in atmospheric carbon dioxide (CO2), capacities for this vary greatly among different tree species and locations. This study compared reactions in the foliage of a deciduous and a coniferous tree species (important central European trees, beech and spruce) to an elevated supply of CO2 and evaluated the importance of the soil type and increased nitrogen deposition on foliar nutrient concentrations and cellular stress reactions. During a period of 4 years, beech (represented by trees from four different regions) and spruce saplings (eight regions), planted together on either acidic or calcareous forest soil in the experimental model ecosystem chambers, were exposed to single and combined treatments consisting of elevated carbon dioxide (+CO2, 590 versus 374 μL L−1) and elevated wet nitrogen deposition (+ND, 50 versus 5 kg ha−1 a−1). Leaf size and foliage mass of spruce were increased by +CO2 on both soil types, but those of beech by +ND on the calcareous soil only. The magnitude of the effects varied among the tree origins in both species. Moreover, the concentration of secondary compounds (proanthocyanidins) and the leaf mass per area, as a consequence of cell wall thickening, were also increased and formed important carbon sinks within the foliage. Although the species elemental concentrations differed in their response to CO2 fertilization, the +CO2 treatment effect was weakened by an acceleration of cell senescence in both species, as shown by a decrease in photosynthetic pigment and nitrogen concentration, discolouration and stress symptoms at the cell level; the latter were stronger in beech than spruce. Hence, young trees belonging to a species with different ecological niches can show contrasting responses in their foliage size, but similar responses at the cell level, upon exposure to elevated levels of CO2. The soil type and its nutrient supply largely determined the fertilization gain, especially in the case of beech trees with a narrow ecological amplitude.
PMCID: PMC4522038  PMID: 26092041
Cell structure; chlorophyll; climate change; condensed tannins; elevated CO2; Fagus sylvatica; mineral nutrition; Picea abies
24.  Meteorological Drivers of Extremes in Daily Stem Radius Variations of Beech, Oak, and Pine in Northeastern Germany: An Event Coincidence Analysis 
Observed recent and expected future increases in frequency and intensity of climatic extremes in central Europe may pose critical challenges for domestic tree species. Continuous dendrometer recordings provide a valuable source of information on tree stem radius variations, offering the possibility to study a tree's response to environmental influences at a high temporal resolution. In this study, we analyze stem radius variations (SRV) of three domestic tree species (beech, oak, and pine) from 2012 to 2014. We use the novel statistical approach of event coincidence analysis (ECA) to investigate the simultaneous occurrence of extreme daily weather conditions and extreme SRVs, where extremes are defined with respect to the common values at a given phase of the annual growth period. Besides defining extreme events based on individual meteorological variables, we additionally introduce conditional and joint ECA as new multivariate extensions of the original methodology and apply them for testing 105 different combinations of variables regarding their impact on SRV extremes. Our results reveal a strong susceptibility of all three species to the extremes of several meteorological variables. Yet, the inter-species differences regarding their response to the meteorological extremes are comparatively low. The obtained results provide a thorough extension of previous correlation-based studies by emphasizing on the timings of climatic extremes only. We suggest that the employed methodological approach should be further promoted in forest research regarding the investigation of tree responses to changing environmental conditions.
PMCID: PMC4891350  PMID: 27375625
dendrometer measurements; event coincidence analysis; climate extremes; growth response
25.  Patterns of late spring frost leaf damage and recovery in a European beech (Fagus sylvatica L.) stand in south-eastern Germany based on repeated digital photographs 
Damage by late spring frost is a risk deciduous trees have to cope with in order to optimize the length of their growing season. The timing of spring phenological development plays a crucial role, not only at the species level, but also at the population and individual level, since fresh new leaves are especially vulnerable. For the pronounced late spring frost in May 2011 in Germany, we studied the individual leaf development of 35 deciduous trees (mainly European beech Fagus sylvatica L.) at a mountainous forest site in the Bayerischer Wald National Park using repeated digital photographs. Analyses of the time series of greenness by a novel Bayesian multiple change point approach mostly revealed five change points which almost perfectly matched the expected break points in leaf development: (i) start of the first greening between day of the year (DOY) 108–119 (mean 113), (ii) end of greening, and (iii) visible frost damage after the frost on the night of May 3rd/4th (DOY 123/124), (iv) re-sprouting 19–38 days after the frost, and (v) full maturity around DOY 178 (166–184) when all beech crowns had fully recovered. Since frost damage was nearly 100%, individual susceptibility did not depend on the timing of first spring leaf unfolding. However, we could identify significant patterns in fitness linked to an earlier start of leaf unfolding. Those individuals that had an earlier start of greening during the first flushing period had a shorter period of recovery and started the second greening earlier. Thus, phenological timing triggered the speed of recovery from such an extreme event. The maximum greenness achieved, however, did not vary with leaf unfolding dates. Two mountain ashes (Sorbus aucuparia L.) were not affected by the low temperatures of -5°C. Time series analysis of webcam pictures can thus improve process-based knowledge and provide valuable insights into the link between phenological variation, late spring frost damage, and recovery within one stand.
PMCID: PMC4338663  PMID: 25759707
Bayesian analysis; digital photography; multiple change point model; phenology; webcam

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